1. Field of the Invention
This invention relates to a muffler hanger adapted for elastically suspending the muffler of the exhaust system of an automotive vehicle, and for absorbing vibration between the muffler and the vehicle body.
2. Description of the Related Art
The function of a muffler hanger of this kind is to prevent up-and-down or vertical vibration of the exhaust system components, including the muffler and exhaust pipe, from being transmitted over to the vehicle body, while at the same time providing elastic support to the suspended muffler. In order to satisfactorily realize this function, the conventional muffler hangers have been designed so as to minimize as much as possible its spring rigidity in the vertical direction, i.e. to make the muffler hangers as flexible as possible in the vertical direction.
FIG. 5 depicts by way of specific example the design disclosed in U.S. Pat. No. 5,050,837. In FIG. 5, 200 denotes a muffler hanger composed of a rubber elastic body having a “θ” shape as a whole. More specifically, the muffler hanger 200 includes: a longwise ellipse-like rubber portion 202 which extend continuously in the circumferential direction; and a connecting rubber portion 204 which interconnects vertically-medial regions of the longwise ellipse-like rubber portion 202 in the left-right direction (i.e. the vehicle left-right direction). In the inside area of the longwise ellipse-like rubber portion 202, an upper space 206 and a lower space 208 are formed respectively to the upper side and the lower side of the connecting portion 204. Upper and lower mounting holes 210, 212 are formed so as to respectively pass through the upper end and the lower end of the rubber annular portion 202 in the front-back direction. In addition, stopper projections 214, 216 are provided for the purpose of limiting excessive displacement of the rubber annular portion 202 in the vertical direction.
This muffler hanger 200 composed of a rubber elastic body is adapted to be attached in the manner depicted in FIG. 5B, so that a support pin 218 on the vehicle body side mates with the upper mounting hole 210 and a support pin 220 on the muffler side mates with the lower mounting hole 212 to elastically support the muffler in the suspended state while providing vibration-absorbing action between the vehicle body and the muffler.
Due to the presence of the upper space 206 and the lower space 208, this muffler hanger 200 as a whole readily gives rise to elastic deformation in the vertical direction. That is, spring rigidity in the vertical direction is low, and accordingly the hanger can flexibly and elastically support the muffler in the vertical direction.
It is difficult for the muffler hanger 200 shown in FIG. 5 to elastically support a muffler by itself. For this reason, when endeavoring to elastically support a muffler using this muffler hanger 200, a pair of the muffler hangers 200 will be disposed on the diagonal in a “V-letter” configuration for use so as to elastically support the muffler 222 as depicted in FIG. 6. The use of a pair of the muffler hangers 200 to elastically support the muffler 222 in this way is disclosed in JP-A-2003-278541.
However, elastically supporting the muffler 222 in this way requires the use of two of the muffler hangers 200, resulting in the problem of an increased number of parts. Also, this muffler 222 creases problems in terms of ride comfort of the vehicle, owing to weak bearing force with respect to motion (swaying) of the muffler 222 in the vehicle left-right direction.
For example, as the vehicle drives through a curve, the vehicle body will sway outward slightly due to centrifugal force. If the bearing force of the muffler hanger 200 in the lateral direction (vehicle left-right direction) is too weak, the muffler 222 will not move in unison with the vehicle body at this time, but will instead move outward after a delay. When the vehicle subsequently exits the curve to resume driving on a straight path, and the vehicle body resumes its original attitude, the muffler will return to its original position after a delay. The movement of the muffler 222 at this time will be transmitted with a delay to the vehicle body, and ride comfort for the persons on the cabin will suffer as a result.
While the muffler hanger 200 depicted in FIGS. 5 and 6 is composed of a rubber elastic body, muffler hangers of designs incorporating metal fittings have been proposed as well. FIG. 7 shows by way of example the hanger disclosed in U.S. Pat. No. 6,739,557.
In FIG. 7, 226 is a metal fitting provided to a muffler hanger 224 and including a mounting plate 229, a pair of side plates 230, and a base plate 232. To the pair of side plates 230, the ends of rubber arms 227 which splay in an inverted “V-letter” configuration are respectively integrally affixed through vulcanization bonding. 228 is a mounting hole.
In the case of the muffler hanger 224 with the metal fitting shown in FIG. 7, since the rubber arms 227 splay in the inverted “V-letter” configuration, even where the hanger is used alone it will be possible for it to elastically support the muffler 222 in similar manner to that shown in FIG. 6. Consequently, the required number of muffler hangers 224 can be reduced. Moreover, the muffler hanger 224 depicted in FIG. 7 affords the advantage of higher bearing force of the muffler 222 in the left-right direction, i.e. higher spring rigidity in the left-right direction, as compared with the one shown in FIGS. 5 and 6.
However, in the case of the muffler hanger 224 with the metal fitting shown in FIG. 7, since the metal fitting 226 is one of the required components, in the process of manufacture of the muffler hanger 224 a vulcanization bonding step will be necessary in order to bond the metal fitting with the rubber arms 227 made of a rubber elastic body, resulting in the problem of a more complex manufacturing process and associated higher cost.
With the muffler hanger 224 depicted in FIG. 7, while spring rigidity in the left-right direction, i.e. bearing force in the left-right direction, is higher compared with that of the hanger shown in FIGS. 5 and 6, it does still not achieve a sufficiently high spring ratio of spring rigidity in the left-right direction to spring rigidity in the vertical direction. This makes it impossible for example to prevent to a sufficient extent the aforementioned problem encountered when the vehicle travels through a curve, while at the same time maintaining low spring rigidity in the vertical direction.
JP-A-62-289428 discloses a muffler hanger directed to addressing this problem. FIG. 8 illustrates a specific example. In FIG. 8, 234 is a muffler hanger made of a rubber elastic body, 236 is a rubber arm of bowed shape, 238 denotes holes for mounting to the vehicle body; 240 is a hole for mounting to the muffler, 242 is a vertical direction stopper portion, and 244 is the floor of the vehicle body.
However, with the muffler hanger 234 shown in FIG. 8, if input occurs in the lateral direction, the rubber arm 236 will experience appreciable shear deformation to absorb the input, and consequently the muffler hanger 234 depicted in FIG. 8 also lacks sufficient spring rigidity in the left-right direction, making it difficult to sufficiently avoid the aforementioned problem encountered when the vehicle travels through a curve.
JP-Y-6-12185 discloses another muffler hanger of a design intended to be fastened through mounting at three points to the vehicle body and to the muffler. However, the hanger disclosed in JP-Y-6-12185 differs from that taught in the present invention.